Mojo: POSIX: Add a PlatformChannelSendmsgWithHandles().

mojo/embedder/platform_channel_utils_posix.h

Index: mojo/embedder/platform_channel_utils_posix.h
diff --git a/mojo/embedder/platform_channel_utils_posix.h b/mojo/embedder/platform_channel_utils_posix.h
index 5146ce5df238509db0290223a7b14506053f80ca..6d0ffcd2de595c707a5e7ff243fb2f0611a16241 100644
--- a/mojo/embedder/platform_channel_utils_posix.h
+++ b/mojo/embedder/platform_channel_utils_posix.h
@@ -20,7 +20,7 @@ namespace mojo {
 namespace embedder {
 
 // The maximum number of handles that can be sent "at once" using
-// |PlatformChannelSendHandles()|.
+// |PlatformChannelSendmsgWithHandles()|.
 // TODO(vtl): This number is taken from ipc/file_descriptor_set_posix.h:
 // |FileDescriptorSet::kMaxDescriptorsPerMessage|. Where does it come from?
 const size_t kPlatformChannelMaxNumHandles = 7;
@@ -36,6 +36,23 @@ MOJO_SYSTEM_IMPL_EXPORT ssize_t PlatformChannelWritev(PlatformHandle h,
                                                       struct iovec* iov,
                                                       size_t num_iov);
 
+// Writes data, and the given set of |PlatformHandle|s (i.e., file descriptors)
+// over the Unix domain socket given by |h| (e.g., created using
+// |PlatformChannelPair()|). All the handles must be valid, and there must be at
+// least one and at most |kPlatformChannelMaxNumHandles| handles. The return
+// value is as for |sendmsg()|, namely -1 on failure and otherwise the number of
+// bytes of data sent on success (note that this may not be all the data
+// specified by |iov|). (The handles are not closed, regardless of success or
+// failure.)
+MOJO_SYSTEM_IMPL_EXPORT ssize_t PlatformChannelSendmsgWithHandles(
+    PlatformHandle h,
+    struct iovec* iov,
+    size_t num_iov,
+    PlatformHandle* platform_handles,
+    size_t num_platform_handles);
+
+// TODO(vtl): Remove this once I've switched things over to
+// |PlatformChannelSendmsgWithHandles()|.
 // Sends |PlatformHandle|s (i.e., file descriptors) over the Unix domain socket
 // (e.g., created using PlatformChannelPair|). (These will be sent in a single
 // message having one null byte of data and one control message header with all